Many devices rely on an energy storage device such as a capacitor to store potential energy and supply a voltage to a load. Examples of such devices include photographic flash lamps and flashing warning lights.
A defibrillator is another device that stores energy, typically in one or more high-voltage capacitors, and delivers the stored energy to a patient. In particular, a defibrillator delivers energy to a heart that is undergoing fibrillation and has lost its ability to contract. Ventricular fibrillation is particularly life threatening because activity within the ventricles of the heart is so uncoordinated that virtually no pumping of blood takes place. An electrical pulse delivered to a fibrillating heart may repolarize the heart and cause it to reestablish a normal sinus rhythm.
Although defibrillators may be internally implanted in patients that suffer from chronic fibrillation, an electric pulse may also be applied externally via paddles placed upon the patient's chest. When a switch is closed, the capacitor sends at least a part of the stored energy from paddle to paddle through the patient's chest. The energy transferred may be on the order of several hundred joules. To achieve this level of energy transfer, the power needed to deliver the energy may be on the order of hundreds of kilowatts and the voltage across the capacitor may be on the order of several thousand volts.
A defibrillator such as a portable defibrillator typically includes a battery, which by itself is not capable of providing the high energy, high-voltage electric pulses required for defibrillation therapy. Instead, the battery is used to charge the high-voltage energy storage capacitors. In a flyback charger, the battery supplies energy to the primary coil of a flyback transformer while a control switch is closed. When the control switch is opened, the energy stored in the primary coil is transferred to the secondary coil of the flyback transformer. The energy is then stored on the storage capacitors, which are coupled to the secondary coil by a diode. By opening and closing the control switch, energy is incrementally transferred from the battery to the capacitors, thereby increasing the energy stored in the capacitors and charging the capacitors to a high voltage.